Model takes off during RRA

[Daniel Kohle]

Hello all,
i have a problem with the RRA-tool. I used Visual 3D to export a model and a motion (a squat jump) to OpenSIM. All runs well until I try to complete RRA. First problem is, that the residuals, especially MX, are extremely high (FX=-9.96437 FY=39.1024 FZ=28.485
MX=-116.667 MY=-0.458137 MZ=-80.7182). Second, during RRA the model takes off the ground long before the "real" jump and levitating in air, the real jump is just the extension of the legs without any movement upwards.
Do you have any ideas what the reasons might be?

Greetings,
Daniel

[Ayman Habib]

Dear Daniel,

Please check the Wiki page for some pointers/ common pitfalls
http://wiki.simtk.org/opensim/rraCmcPage

In general, with proper setup and arbitrarily large residuals, RRA should be able to reproduce the motion exactly.

Good Luck,
-Ayman

[Daniel Kohle]

I'm new to OpenSim but I think that I followed all these instructions to make RRA run. Though I still have this taking off. What could cause the large residuals?

[Daniel Leib]

Hi Daniel,

It almost sounds like your force data and kinematic data are out of sync; are you certain that differing sampling rates are not at fault? Does the model begin to move upwards at a time point that might make sense in this context?

Have a good one,

-Dan

[Daniel Kohle]

I'm sure that the data is synchronized well. Inverse Dynamics give me good results. And I exported GRF and kinematics directly out of Visual3D, it was recorded in one file. So I don't think that this could cause my problems, do you?

I now tried to perform CMC without RRA. The result is the same: The model takes off and just extends its leg in the air. I tried to vary the masses of torso and pelvis to see whether there is any mistake and also extended the clamps of the residuals and forces in the configuration files.

Perhaps one fact helps solving this: OpenSim is not able to filter my GRF-data. When I chose this option in the CMC-tool, I directly get an error (something like "Infeasable..."). Without filtering the tool begins to solve the RRA-algorithm (but model takes off).

[Daniel Leib]

Hi Daniel,

I haven't used V3D to export the data yet personally - is there a pipeline command specifically for this or did you just export a text file and alter the format? I'm interested in using V3D as well for export but haven't had a chance to play with it much yet.

Thanks,

Dan

[Daniel Kohle]

Dan:
The actual published version of V3D isn't able to export to OpenSim, but the current beta can do this with some limitations. In that case, V3D creates a mov-File and a scale-set, which you can add to an existing model in OpenSim. V3D "overrides" the inverse kinematics of OpenSim and uses its own. So, after exporting, you just need to scale your model to prepare it for RRA and CMC.
Greetings,
Daniel

[Daniel Kohle]

I figured out some more about my problem. Perhaps anyone of you can help me afterwards: When I run RRA in small intervals (0.25 seconds), I can solve it without taking off. But when I try to solve the whole interval (about 2 seconds), the mistake occurs. What could cause this?

[Daniel Leib]

Have you played with the integrator settings? The default number of steps is 20k - if you use 0.25 seconds as opposed to 2 seconds, it will use up to the same number of steps regardless. Try increasing this and see if it doesn't stabilize your model; I've had luck with this in the past.

Have a good one,

Dan

[Daniel Kohle]

I tried to do that. I ran RRA over a 1.2-second interval with 160k integration steps. Nevertheless the model starts to hover. I will increase the steps a little more but I don't think that this will solve the problem.
- Daniel